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虚拟语气
与过去事实相反的虚拟：
If + had done + ..., ... would (might) have done ...
If I had known your telephone number yesterday, I would have phoned you.
(I didn't know your telephone number.)
If you had come here a littleearlier just now, you might have met her.
(You didn't come here earlier.)
2.Police in Northern Ireland say a bomb discovered in a car at Belfast International Airport at the weekend could have been there since last year.
这句话的主语和谓语是：Police in Northern Ireland say，后面是宾语从句。宾语从句的主干是：a bomb could have been。could have been表示猜测。
